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Press the input and see what keycode are generated. There will be three different kind of events will be generated KEY-UP, KEY-DOWN and KEY-PRESS.
Take a note of code and try to find the corresponding output code from this. Finding output code is sometimes a big task as it could be dependent on various parameters.
For details refer [1].
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These values are taken from display_name column in guest_os table. To see current list of guest os available refer the CloudStack documents. Or this can be seen from os OS Type in template details or while registering template
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